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Overfill Prevention Equipment Inspection

The Overfill Prevention Equipment Inspection is a task in the Underground Storage Tank compliance program.


One of the easiest ways for a tank system to have a release is during filling. If the delivery volume exceeds the empty volume, the excess volume can end up on the tank pad, and pollute public streets and stormwater systems.  Overfill prevention equipment is designed to prevent overfill accidents. All California USTs must have overfill protection equipment and it must be tested at least every three years to verify proper operation.

Types of overfill prevention

There are four kinds of overfill protection:

  1. A system that alerts the delivery driver that the tank is 90 percent full by restricting the flow or triggering an audible and visual alarm.
  2. A system that restricts the flow to the tank at least 30 minutes before the tank overfills. The restriction must begin at or before the tank is 95 percent full. The system must also incorporate an audible alarm that activates no later than 5 minutes before the tank overfills.
  3. A system that provides positive shut-off of flow to the tank when it is no more than 95 percent full.
  4. A system that provides positive shut-off of flow so the tank’s top mounted fittings  are not exposed to located on the top of the tank are exposed to product due to overfilling.

Overfill prevention exemptions

The unified program agency may waive the requirement for overfill prevention equipment where:

  • the tank inlet is observable,
  • the spill container is adequate to collect any overfill,
  • the tank system is filled with no more than 25 gallons at a time.

Note: As of October 13, 2018 flow restrictors on vent piping (ball floats) can no longer be allowed to be installed or repaired. (If an existent ball float fails during testing, it needs to be replaced by another overfill prevention system.)

Note: manual overrides are not allowed on overfill prevention equipment.

Overfill Prevention Equipment Inspections

UST Overfill Prevention Equipment Testing
Appendix IX UST Overfill Prevention Equipment Inspection

Exiting USTs must test overfill prevention equipment on or before October 13, 2018 and every 36 months thereafter.

Operators of USTs must also test overfill prevention equipment:

  • Within 30 days of the completion of a repair.
  • Upon the installation of a new UST system and every 36 months thereafter.

Additional requirements of the overfill prevention equipment inspection include:


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